This invention relates generally to a method and device for determining the degree of aged deterioration of a paint film formed on the surface of a metal member of an equipment, and more particularly to such a paint film deterioration diagnosing method and device wherein the degree of deterioration of the paint film is determined from an impedance of the paint film.
A paint film is usually formed on the outer surface of an equipment installed outdoors, for example, transformers or switchboards for the purposes of corrosion prevention, appearance improvement and the like. It is known in the art that the paint film formed on the outer surface of the equipment is deteriorated with time at different speeds depending upon environment of the equipment. When the paint film is left deteriorated, corrosion of a base metal covered by the paint film finally causes flaking of the paint film and occurrence of rust. The equipment needs to be repainted at an appropriate time for maintenance thereof so that a new paint film is formed on the outer surface of the equipment. When repainting is carried out too early, it results in wasting the cost therefor. When repainting is carried out too late, an economic burden is increased since repair of the corroded base metal takes much time. Thus, when an opportunity for repainting is missed, a bad influence is exerted on the maintenance of the equipment. Conventionally, in the above-mentioned equipments, the degree of deterioration of the paint film is periodically diagnosed so that an appropriate opportunity for repainting is determined.
It is desirable that the result of the above-mentioned diagnosis should have as much objectivity as possible or an appropriate determination should always be made no matter who carries out the diagnosis. In consideration of this point, the prior art has provided the following method of diagnosing the deterioration of the paint film. A large number of sample photographs are previously prepared which show different stages of deterioration with respect to various conditions of deterioration such as peeling, cracking, blistering, rusting and the like. The paint film to be actually diagnosed is compared with the sample photographs by a workman engaged in the diagnosis. The workman understands what stages of the sample photographs the condition of the paint film to be diagnosed corresponds to with respect to various conditions of deterioration and further, assigns predetermined scores with respect to various conditions and degrees of deterioration. The scores are sequentially added. When the value obtained from addition of scores reaches a predetermined value, it is determined by the workman that repainting or repair and repainting should be carried out.
The prior art has provided another method of diagnosing the paint film deterioration, which method is somewhat in advance of the above-described one. This method makes use of an impedance of the paint film varied depending upon the degree of deterioration. This method is disclosed in Japanese Laid-open (kokai) Patent Application No. 62-102148 (1987) filed by the assignee of the present application, for example. An actually employed diagnosis procedure in accordance with this method is summarized as follows. An impedance measurement device is brought into a place where the equipment as an object to be diagnosed is installed. A probe is applied to the surface of the paint film and voltages at various frequencies are applied across the probe and a base metal on which the paint film is formed. The paint film impedance values measured based on the currents flowing as the result of voltage application are read by the workman to be written down. The resistive and capacitive impedance values written down with respect to various frequencies are compared with a previously prepared list for determining what columns in the list the impedance values correspond to, thereby determining the degree of the paint film deterioration. The frequency for measuring the paint film impedance is usually 200 Hz, 500 Hz or 1 KHz.
In the former method, however, the determination to which of the sample photographs the actual degree of the paint film deterioration corresponds tends to be influenced by the subjectivity of the workman engaged in the diagnosis. Thus, this method cannot warrant that every workman can always carry out an appropriate diagnosis. Accordingly, the result of the diagnosis is not likely to be highly esteemed and therefore, repainting or repair of the equipment with painting is not carried out at an appropriate time. Furthermore, this method necessitates for the workman to compare the actual paint film with a number of sample photographs and to add the scores. These works are troublesome and miscalculations can occur in adding the scores.
On the other hand, in the latter method in which the impedance of the paint film is measured, there is a possibility that readings of measured values may be influenced by the operator's subjectivity. Additionally, it is troublesome to compare the measured values with criterion for evaluation.